The invention relates to base supports or mounting assemblies for movable antennae, especially communications dish antennae such as dish antennae for audio, video or data signals.
It is well known that a satellite antenna may be mounted on a support having relatively movable parts which allow the antenna to be aimed toward a particular satellite in geostationary orbit above the earth to collect signals relayed and/or transmitted from that satellite. A description of the general operation of dish antennae and the relationship thereof to orbiting satellites beaming signals to such antennae is contained in my U.S. Pat. No. 4,617,572, issued Oct. 14, 1986, the disclosure of which is incorporated herein by reference thereto.
As is described in U.S. Pat. No. 4,617,572 it is known to provide a base support for a dish antenna having vertical adjusting means to adjust the position of the antenna along a vertical plane to direct the antenna toward the "Clark belt" or "geostationary satellite belt." Thereafter, horizontal adjustment means on the base support, including a reversible motor may be used to scan back and forth along the satellite belt until desired signals from a particular satellite are clearly being received by the dish antenna.
According to my prior patent, as most clearly shown in FIGS. 2, and 5-7 thereof, a reversible electric motor 52 drives a worm W which is in intermeshing contact with a worm gear, referred to in my prior patent as a 180.degree. quadrant gear, 50. The motor 52 is mounted stationery in the horizontal plane, while revolution of worm W will cause worm gear 50 to move in the horizontal plane, thus repositioning the attached dish antenna. It can readily be seen that this structure permits only 180.degree. movement of the dish antenna since worm gear 50 only extends 180.degree. around the vertical support shaft of the antenna. Further, even if gear 50 were extended completely around the vertical support shaft, stationary motor 52 would obstruct full 360.degree. rotation of the antenna. While 360.degree. rotation of a home television dish antenna is not normally necessary due to the permanent installation of the dish support and the equatorial location of the satellite belt, such full rotation is desirable for mobile satellite antennae such as are used on recreational vehicles, mobile news vans or the like. Also in the past, multiple 360.degree. revolutions of a mobile antenna would necessitate the inclusion of relatively expensive electrical interface slip rings.
It has also been found that since home satellite antennae are normally set for relatively long periods of time in only a few horizontal positions corresponding to the satellite beams available, the worm gear 50 is subject to uneven wear. More specifically, when worm W is stopped, the intermeshing of worm W with gear 50 is the only means utilized to maintain the precise positioning of the antenna. In the positions most used; that is, the positions where the helical tooth of worm W most often statically contacts a small number of the teeth of gear 50, the teeth of the gears may experience greater or uneven wear. When this occurs, backlash between the worm and the worm gear may be experienced producing loose intermeshing contact between worm W and gear 50 at some or all of the relative positions. This backlash may cause the antenna to vibrate when completely motionless stability is required for best performance.
Another problem which may be experience in my prior art mechanism is that if dirt or a rock should become lodged between adjacent teeth of gear 50, the system may become jammed when worm W comes in contact with the obstruction.